RFID reader discipline

ABSTRACT

A method for coordinating reader transmissions, according to one embodiment, includes: at a first reader, receiving from a second reader a request to transmit to a RFID tag; determining whether the first reader is transmitting; and sending a denial of the request from the first reader to the second reader in response to determining that the first reader is transmitting. A method, according to another embodiment, includes: from a first reader, sending to a plurality of readers a request to transmit to a RFID tag; waiting for responses from the plurality of readers; not transmitting to the RFID tag in response to the first reader receiving a denial of the request from any of the readers; and transmitting to the RFID tag in response to the first reader not receiving a denial of the request from any of the readers. Additional systems, methods and computer program products are presented.

FIELD OF THE INVENTION

The present invention relates to Radio Frequency (RF) devices, and moreparticularly, this invention relates to RF systems and methods toeliminate interference between RF devices.

BACKGROUND OF THE INVENTION

The use of Radio Frequency Identification (RFID) tags are quicklygaining popularity for use in the monitoring and tracking of an item.RFID technology allows a user to remotely store and retrieve data inconnection with an item utilizing a small, unobtrusive tag. As an RFIDtag operates in the radio frequency (RF) portion of the electromagneticspectrum, an electromagnetic or electrostatic coupling can occur betweenan RFID tag affixed to an item and an RFID tag reader. This coupling isadvantageous, as it precludes the need for a direct contact or line ofsight connection between the tag and the reader.

RF devices in proximity to each other can interfere with each otherunless there is a method of coordinating their operation. Thisinterference can render the RF devices inoperable. One currently usedmethod to avoid this interference is to have all devices attached, insome way, to a central coordinating device. This method is called readerorchestration. Reader orchestration introduces additional requirementsand complexity in the central coordinating device and in theapplications that are attempting to use the RF devices' capabilities.This method also introduces a single point of failure into the system.Therefore, it would be advantageous to have a method which could beintegrated into each RF device to overcome interference issues betweenRF devices without using a central coordinating device.

SUMMARY OF THE INVENTION

A method for coordinating reader transmissions, according to oneembodiment, includes: at a first reader, receiving from a second readera request to transmit to a RFID tag; in response to receiving therequest, determining whether the first reader is transmitting; andsending a denial of the request from the first reader to the secondreader in response to determining that the first reader is transmitting.

A method for coordinating reader transmissions, according to anotherembodiment, includes: from a first reader, sending to a plurality ofreaders a request to transmit to a RFID tag, the request being directedto the readers; waiting for responses from the plurality of readers; nottransmitting to the RFID tag in response to the first reader receiving adenial of the request from any of the readers; and transmitting to theRFID tag in response to the first reader not receiving a denial of therequest from any of the readers.

A method for coordinating reader transmissions, according to yet anotherembodiment, includes: for a first of a plurality of readers, determiningwhether the first reader and any other of the readers interfere witheach other; and storing a result of the determination; wherein the firstreader sends a request to transmit to those readers determined tointerfere with the first reader or vice versa prior to transmitting to aRFID tag, the request to transmit being directed to those readersdetermined to interfere with the first reader or vice versa; wherein thefirst reader does not transmit to the RFID tag in response to the firstreader receiving a denial of the request from any of the readers therequest was sent to; and wherein the first reader transmits to the RFIDtag in response to the first reader not receiving a denial of therequest from any of the readers the request was sent to.

A system, according to one embodiment, includes: a processing circuit;memory coupled to the processing circuit; and an antenna coupled to theprocessing circuit, wherein the processing circuit is configured to: ata first reader, receive from a second reader a request to transmit to aRFID tag; and send a denial of the request from the first reader to thesecond reader when the first reader is transmitting upon receiving therequest from the second reader.

A computer program product, according to one embodiment, includes anon-transitory computer readable medium having computer code thereon,which when executed by a reader causes the reader to: receive, by thereader, a request to transmit to a RFID tag from a remote reader; andsend, by the reader, a denial of the request to the remote reader whenthe reader is transmitting upon receiving the request from the remotereader.

A system, according to another embodiment, includes: a processingcircuit; memory coupled to the processing circuit; and an antennacoupled to the processing circuit, wherein the processing circuit isconfigured to: from a first reader, send to a plurality of readers arequest to transmit to a RFID tag, the request being directed to thereaders; wait for responses from the plurality of readers; not transmitto the RFID tag in response to the first reader receiving a denial ofthe request from any of the readers; and transmit to the RFID tag inresponse to the first reader not receiving a denial of the request fromany of the readers.

A computer program product, according to another embodiment, includes anon-transitory computer readable medium having computer code thereon,which when executed by a reader causes the reader to: send to aplurality of readers a request to transmit to a RFID tag, the requestbeing directed to the readers; wait for responses from the plurality ofreaders; not transmit to the RFID tag in response to the first readerreceiving a denial of the request from any of the readers; and transmitto the RFID tag in response to the first reader not receiving a denialof the request from any of the readers.

A system, according to yet another embodiment, includes: a processingcircuit; memory coupled to the processing circuit; and an antennacoupled to the processing circuit, wherein the processing circuit isconfigured to: determine whether a first of a plurality of readers andany other of the readers interfere with each other; store a result ofthe determination; store a request to transmit from the first reader tothose readers determined to interfere with the first reader or viceversa prior to transmitting to a RFID tag, the request to transmit beingdirected to those readers determined to interfere with the first readeror vice versa; not transmit to the RFID tag in response to the firstreader receiving a denial of the request from any of the readersreceiving the request; and transmit to the RFID tag in response to thefirst reader not receiving a denial of the request from any of thereaders receiving the request.

A computer program product, according to yet another embodiment,includes a non-transitory computer readable medium having computer codethereon, which when executed by a reader causes the reader to: determinewhether a first of a plurality of readers and any other of the readersinterfere with each other; and store a result of the determination; senda request to transmit from the first reader to those readers determinedto interfere with the first reader or vice versa prior to transmittingto a RFID tag, the request to transmit being directed to those readersdetermined to interfere with the first reader or vice versa; nottransmit to the RFID tag in response to the first reader receiving a ofthe request from any of the readers receiving the request; and transmitto the RFID tag in response to the first reader not receiving a denialof the request from any of the readers receiving the request.

Any of these embodiments may be implemented in an RFID system, which mayinclude an RFID tag and/or interrogator.

Other aspects, advantages and embodiments of the present invention willbecome apparent from the following detailed description, which, whentaken in conjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a system diagram of an RFID system.

FIG. 2A is a system diagram for an integrated circuit (IC) chip forimplementation in an RFID device.

FIG. 2B is a simplified diagram of a network that can include RFIDdevices.

FIG. 3 is a flow chart of a method for coordinating reader transmissionsaccording to one embodiment.

FIG. 4 is a flow chart of a method for coordinating reader transmissionsaccording to one embodiment.

FIG. 5 is a flow chart of a method for coordinating reader transmissionsaccording to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

In one general embodiment, a method for coordinating readertransmissions includes: at a first reader, receiving from a secondreader a request to transmit to a RFID tag; in response to receiving therequest, determining whether the first reader is transmitting; andsending a denial of the request from the first reader to the secondreader in response to determining that the first reader is transmitting.

In another general embodiment, a method for coordinating readertransmissions includes: from a first reader, sending to a plurality ofreaders a request to transmit to a RFID tag, the request being directedto the readers; waiting for responses from the plurality of readers; nottransmitting to the RFID tag in response to the first reader receiving adenial of the request from any of the readers; and transmitting to theRFID tag in response to the first reader not receiving a denial of therequest from any of the readers.

In yet another general embodiment, a method for coordinating readertransmissions includes: for a first of a plurality of readers,determining whether the first reader and any other of the readersinterfere with each other; and storing a result of the determination;wherein the first reader sends a request to transmit to those readersdetermined to interfere with the first reader or vice versa prior totransmitting to a RFID tag, the request to transmit being directed tothose readers determined to interfere with the first reader or viceversa; wherein the first reader does not transmit to the RFID tag inresponse to the first reader receiving a denial of the request from anyof the readers the request was sent to; and wherein the first readertransmits to the RFID tag in response to the first reader not receivinga denial of the request from any of the readers the request was sent to.

In one general embodiment, a system includes: a processing circuit;memory coupled to the processing circuit; and an antenna coupled to theprocessing circuit, wherein the processing circuit is configured to: ata first reader, receive from a second reader a request to transmit to aRFID tag; and send a denial of the request from the first reader to thesecond reader when the first reader is transmitting upon receiving therequest from the second reader.

In another general embodiment, a computer program product includes anon-transitory computer readable medium having computer code thereon,which when executed by a reader causes the reader to: receive, by thereader, a request to transmit to a RFID tag from a remote reader; andsend, by the reader, a denial of the request to the remote reader whenthe reader is transmitting upon receiving the request from the remotereader.

In another general embodiment, a system includes: a processing circuit;memory coupled to the processing circuit; and an antenna coupled to theprocessing circuit, wherein the processing circuit is configured to:from a first reader, send to a plurality of readers a request totransmit to a RFID tag, the request being directed to the readers; waitfor responses from the plurality of readers; not transmit to the RFIDtag in response to the first reader receiving a denial of the requestfrom any of the readers; and transmit to the RFID tag in response to thefirst reader not receiving a denial of the request from any of thereaders.

In another general embodiment, a computer program product includes anon-transitory computer readable medium having computer code thereon,which when executed by a reader causes the reader to: send to aplurality of readers a request to transmit to a RFID tag, the requestbeing directed to the readers; wait for responses from the plurality ofreaders; not transmit to the RFID tag in response to the first readerreceiving a denial of the request from any of the readers; and transmitto the RFID tag in response to the first reader not receiving a denialof the request from any of the readers.

In yet another general embodiment, a system includes: a processingcircuit; memory coupled to the processing circuit; and an antennacoupled to the processing circuit, wherein the processing circuit isconfigured to: determine whether a first of a plurality of readers andany other of the readers interfere with each other; store a result ofthe determination; store a request to transmit from the first reader tothose readers determined to interfere with the first reader or viceversa prior to transmitting to a RFID tag, the request to transmit beingdirected to those readers determined to interfere with the first readeror vice versa; not transmit to the RFID tag in response to the firstreader receiving a denial of the request from any of the readersreceiving the request; and transmit to the RFID tag in response to thefirst reader not receiving a denial of the request from any of thereaders receiving the request.

In yet another general embodiment, a computer program product includes anon-transitory computer readable medium having computer code thereon,which when executed by a reader causes the reader to: determine whethera first of a plurality of readers and any other of the readers interferewith each other; and store a result of the determination; send a requestto transmit from the first reader to those readers determined tointerfere with the first reader or vice versa prior to transmitting to aRFID tag, the request to transmit being directed to those readersdetermined to interfere with the first reader or vice versa; nottransmit to the RFID tag in response to the first reader receiving a ofthe request from any of the readers receiving the request; and transmitto the RFID tag in response to the first reader not receiving a denialof the request from any of the readers receiving the request.

FIG. 1 depicts an RFID system 100 according to one of the variousembodiments, which may include some or all of the following componentsand/or other components. As shown in FIG. 1, one or more RFID devices102 are present. Each RFID device 102 in this embodiment includes acontroller and memory, which are preferably embodied on a single chip asdescribed below, but may also or alternatively include a different typeof controller, such as an application specific integrated circuit(ASIC), processor, an external memory module, etc. For purposes of thepresent discussion, the RFID devices 102 will be described as includinga chip. Each RFID device 102 may further include or be coupled to anantenna 105.

An illustrative chip is disclosed below, though actual implementationsmay vary depending on how the device is to be used. In general terms, apreferred chip includes one or more of a power supply circuit to extractand regulate power from the RF reader signal; a detector to decodesignals from the reader; a backscatter modulator, a transmitter to senddata back to the reader; anti-collision protocol circuits; and at leastenough memory to store its unique identification code, e.g., ElectronicProduct Code (EPC).

While RFID devices 102 according to some embodiments are functional RFIDtags, other types of RFID devices 102 include merely a controller withon-board memory, a controller and external memory, etc.

Each of the RFID devices 102 may be coupled to an object or item, suchas an article of manufacture, a container, a device, a person, etc.

With continued reference to FIG. 1, a remote device 104 such as aninterrogator or “reader” communicates with the RFID devices 102 via anair interface, preferably using standard RFID protocols. An “airinterface” refers to any type of wireless communications mechanism, suchas the radio-frequency signal between the RFID device and the remotedevice. The RFID device 102 executes the computer commands that the RFIDdevice 102 receives from the remote device 104 (e.g., reader).

The system 100 may also include an optional backend system such as aserver 106, which may include databases containing information and/orinstructions relating to RFID tags and/or tagged items.

As noted above, each RFID device 102 may be associated with a uniqueidentifier. Such identifier is preferably an EPC code. The EPC is asimple, compact identifier that uniquely identifies objects (items,cases, pallets, locations, etc.) in the supply chain. The EPC is builtaround a basic hierarchical idea that can be used to express a widevariety of different, existing numbering systems, like the EAN.UCCSystem Keys, UID, VIN, and other numbering systems. Like many currentnumbering schemes used in commerce, the EPC is divided into numbers thatidentify the manufacturer and product type. In addition, the EPC uses anextra set of digits, a serial number, to identify unique items. Atypical EPC number contains:

-   -   1. Header, which identifies the length, type, structure, version        and generation of EPC;    -   2. Manager Number, which identifies the company or company        entity;    -   3. Object Class, similar to a stock keeping unit or SKU; and    -   4. Serial Number, which is the specific instance of the Object        Class being tagged.        Additional fields may also be used as part of the EPC in order        to properly encode and decode information from different        numbering systems into their native (human-readable) forms.

Each RFID device 102 may also store information about the item to whichcoupled, including but not limited to a name or type of item, serialnumber of the item, date of manufacture, place of manufacture, owneridentification, origin and/or destination information, expiration date,composition, information relating to or assigned by governmentalagencies and regulations, etc. Furthermore, data relating to an item canbe stored in one or more databases linked to the RFID tag. Thesedatabases do not reside on the tag, but rather are linked to the tagthrough a unique identifier(s) or reference key(s).

RFID systems may use reflected or “backscattered” radio frequency (RF)waves to transmit information from the RFID device 102 to the remotedevice 104, e.g., reader. Since passive (Class-1 and Class-2) tags getall of their power from the reader signal, the tags are only poweredwhen in the beam of the remote device 104.

The Auto ID Center EPC-Compliant tag classes are set forth below:

Class-1

-   -   Identity tags (RF user programmable, range ˜3 m)    -   Lowest cost

Class-2

-   -   Memory tags (20 bit address space programmable at ˜3 m range)    -   Security & privacy protection    -   Low cost

Class-3

-   -   Semi-passive tags (also called semi-active tags and battery        assisted passive (BAP) tags)    -   Battery tags (256 bits to 2M words)    -   Self-Powered Backscatter (internal clock, sensor interface        support)    -   ˜100 meter range    -   Moderate cost

Class-4

-   -   Active tags    -   Active transmission (permits tag-speaks-first operating modes)    -   ˜300 to ˜1,000 meter range    -   Higher cost

In RFID systems where passive receivers (i.e., Class-1 and Class-2 tags)are able to capture enough energy from the transmitted RF to power thedevice, no batteries are necessary. In systems where distance preventspowering a device in this manner, an alternative power source must beused. For these “alternate” systems (e.g., semi-active, semi-passive orbattery-assisted), batteries are the most common form of power. Thisgreatly increases read range, and the reliability of tag reads, becausethe tag does not need power from the reader to respond. Class-3 tagsonly need a 5 mV signal from the reader in comparison to the 500 mV thatClass-1 and Class-2 tags typically need to operate. This 100:1 reductionin power requirement along with the reader's ability to sense a verysmall backscattered signal permits Class-3 tags to operate out to a freespace distance of 100 meters or more compared with a Class-1 range ofonly about 3 meters. Note that semi-passive and active tags with builtin passive mode may also operate in passive mode, using only energycaptured from an incoming RF signal to operate and respond, at a shorterdistance up to 3 meters.

Active, semi-passive and passive RFID tags may operate within variousregions of the radio frequency spectrum. Low-frequency (30 KHz to 500KHz) tags have low system costs and are limited to short reading ranges.Low frequency tags may be used in security access and animalidentification applications for example. Ultra high-frequency (860 MHzto 960 MHz and 2.4 GHz to 2.5 GHz) tags offer increased read ranges andhigh reading speeds.

A basic RFID communication between an RFID device and a remote devicetypically begins with the remote device, e.g., reader, sending outsignals via radio wave to find a particular RFID device, e.g., tag viasingulation or any other method known in the art. The radio wave hitsthe RFID device, and the RFID device recognizes the remote device'ssignal and may respond thereto. Such response may include exiting ahibernation state, sending a reply, storing data, etc.

Embodiments of the RFID device are preferably implemented in conjunctionwith a Class-3 or higher Class IC chip, which typically contains theprocessing and control circuitry for most if not all tag operations.FIG. 2A depicts a circuit layout of a module 200, which may be a Class-3IC, along with the various control circuitry according to anillustrative embodiment for implementation in an RFID tag 102. It shouldbe kept in mind that the present invention can be implemented using anytype of RFID device, and the module 200 circuitry is presented as onlyone possible implementation.

The Class-3 IC of FIG. 2A can form the core of RFID chips appropriatefor many applications such as identification of pallets, cartons,containers, vehicles, or anything where a range of more than 2-3 metersis desired. As shown, the module 200 includes several circuits includinga power generation and regulation circuit 202, a digital command decoderand control circuit 204, a sensor interface module 206, a C1G2 interfaceprotocol circuit 208, and a power source (battery) 210. A display drivermodule 212 can be added to drive a display.

A forward link AM decoder 216 uses a simplified phase-lock-looposcillator that requires only a small amount of chip area. Preferably,the circuit of the decoder 216 requires only a minimum string ofreference pulses.

A backscatter modulator block 218 preferably increases the backscattermodulation depth to more than 50%.

A memory cell, e.g., EEPROM, is also present, and preferably has acapacity from several kilobytes to one megabyte or more. In oneembodiment, a pure, Fowler-Nordheim direct-tunneling-through-oxidemechanism 220 is present to reduce both the WRITE and ERASE currents toabout 2 μA/cell in the EEPROM memory array. Unlike any RFID tags builtto date, this permits reliable tag operation at maximum range even whenWRITE and ERASE operations are being performed. In other embodiments,the WRITE and ERASE currents may be higher or lower, depending on thetype of memory used and its requirements.

Preferably, the amount of memory available on the chip or otherwise isadequate to store data such that the external device need not be inactive communication with the remote device.

The module 200 may also incorporate a security encryption circuit 222for operating under one or more security schemes, secret handshakes withreaders, etc.

The RFID device may have a dedicated power supply, e.g. battery; maydraw power from a power source of the electronic device (e.g., battery,AC adapter, etc.); or both. Further, the RFID device may include asupplemental power source. Note that while the present descriptionrefers to a “supplemental” power source, the supplemental power sourcemay indeed be the sole device that captures energy from outside the tag,be it from solar, RF, kinetic, etc. energy.

Note that while the foregoing has been described in terms of asemi-passive tag, various embodiments may be used in conjunction withpassive as well as active tags.

When RF devices, including RFID readers, try to communicate at the sametime, they may cause interference which may render effectivecommunication between the RF devices difficult or impossible. Readerdiscipline, according to one embodiment, requires no central controllingdevice, as is used in reader orchestration. Also, according to anotherembodiment, reader discipline does not require the applications seekingto take advantage of the RF devices' capabilities to be cognizant of anyother demands being made on the system. Therefore, in this embodiment,the author of the application is not required to implement a second setof application programming interface (API) calls, as would be requiredif the application had to communicate with a central coordinatingdevice. The application writer can treat the system as if he is the onlyuser of the system, greatly simplifying the work required to implementany particular function. This embodiment has the further advantages thatthe overall performance of the system may be optimized: first, becauseit avoids the bottleneck of the central coordinating device; and second,the RF devices each know the real time demand, and can reorder theiroperations optimally. Legacy applications and applications not writtento the central coordinating device's API would interfere with the readerorchestration technique. However, reader discipline, according to someembodiments, does not require any change in the application. Readerorchestration forces a system to use a single API while readerdiscipline, in some embodiments, would allow any and all API's to worktogether.

FIG. 2B illustrates a network architecture 250, in accordance with oneembodiment. As shown, a plurality of networks 252 is provided. In thecontext of the present network architecture 250, the networks 252 mayeach take any form including, but not limited to a local area network(LAN), a wireless network, a wide area network (WAN) such as theInternet, peer-to-peer network, etc.

Coupled to the networks 252 are servers 254 which are capable ofcommunicating over the networks 252. Also coupled to the networks 252and the servers 254 is a plurality of clients 256. Such servers 254and/or clients 256 may each include a desktop computer, lap-topcomputer, hand-held computer, RFID device 102 including RFID tags,mobile phone, smart phone and other types of mobile media devices (withor without telephone capability), personal digital assistant (PDA),peripheral (e.g. printer, etc.), any component of a computer, and/or anyother type of logic. In order to facilitate communication among thenetworks 252, at least one gateway 258 is optionally coupledtherebetween.

Now referring to FIG. 3, in one embodiment, a method 300 forcoordinating reader transmissions is shown. As an option, the presentmethod 300 may be implemented in the context of the functionality andarchitecture of FIGS. 1, 2A, and 2B. Of course, the method 300 may becarried out in any desired environment. It should also be noted that theaforementioned definitions may apply during the present description. Inoperation 302, at a first reader, a request to transmit to an RFID tagis received from a second reader. In another approach, the request totransmit to an RFID tag may be received from some other RF device.

In operation 304, if the first reader is transmitting, a denial of therequest from the first reader is sent to the second reader. This denialmay preempt the second reader from transmitting, or it may invoke aresponse from the second reader that may be sent to the first reader, orsome other device.

In other embodiments, the readers may communicate directly with eachother via RF signal and/or network using standard or proprietaryprotocols. For example, the readers may send requests and denialsdirectly to each other via RF signals, or they may send requests anddenials directly to each other via a network. A network may includehardwired and/or wireless components.

In another embodiment, the first reader may send a completion notice tothe second reader upon completion of the transmitting. The completionnotice may be sent once or multiple times over a predetermined time. Inaddition, the completion notice may contain other information that canbe useful in reader discipline, such as which reader should transmitnext, which readers are currently waiting to transmit, etc.

In yet another embodiment, the second reader may transmit to the RFIDtag if no denial of the request is received after a predetermined amountof time has elapsed since the second reader transmitted the request totransmit. In another approach, the second reader may send out requeststo transmit to the RFID tag at predetermined intervals until it receivesno denial from the first reader.

In still another embodiment, the first and second readers may receive arequest to transmit from a third reader, where the first reader may betransmitting and the second reader may be waiting to transmit, and eachmay send a denial of the third reader's request. Further, the thirdreader may wait until the second reader completes transmission beforeattempting to communicate with an RFID tag. In another approach, thefirst and second readers may receive a request to transmit from a thirdreader, where the second reader may be transmitting and the first readermay be waiting to transmit, and each may send a denial of the thirdreader's request. The third reader may wait until the first readercompletes transmission before attempting to communicate with an RFIDtag. In yet another approach, the third reader may send requests atpredetermined time intervals until it does not receive a denial from thefirst or second reader before transmitting to an RFID tag.

In another approach, the first and second readers may receive a requestto transmit from a third reader, where the request from the third readermay include a request for priority, where if the first reader istransmitting and the second reader is waiting to transmit, the firstreader may abort transmitting and the second reader may wait to transmitto the RFID tag until after the third reader communicates with an RFIDtag. In another approach, the second reader may be transmitting and thefirst reader may be waiting, and the request from the third reader mayinclude a request for priority, where if the second reader istransmitting and the first reader is waiting to transmit, the secondreader may abort transmitting and the first reader may wait to transmitto the RFID tag until after the third reader communicates with an RFIDtag. In addition, the request for priority may be in compliance with apreset priority level, such as a priority table, where differentrequests for priority have different levels have priority, such that areader transmitting at a higher priority level will not be interruptedif the request for priority received from another reader is of a lowerpriority level based on the priority table.

In yet another approach, the first and second readers may receive arequest to transmit from a third reader. The request from the thirdreader may include a request for priority. If the first reader istransmitting and the second reader is waiting to transmit, the firstreader may send a denial of the third reader's request, and the secondreader may wait to transmit to the RFID tag until after the third readercommunicates with an RFID tag.

With reference to FIG. 4, a method 400 for coordinating readertransmissions is shown according to one embodiment. As an option, thepresent method 400 may be implemented in the context of thefunctionality and architecture of FIGS. 1, 2A, and 2B. Of course, themethod 400 may be carried out in any desired environment. It should alsobe noted that the aforementioned definitions may apply during thepresent description. In operation 402, a request from a first reader issent to a plurality of readers to transmit to an RFID tag.

In operation 404, responses from the plurality of readers are waitedfor. For example, the first reader may wait for a predetermined amountof time to receive a denial of the request to transmit to an RFID tag.

In operation 406, if a denial of the request is received by the firstreader from any of the readers, no transmission is made to the RFID tag.In another approach, the first reader may send out requests to transmitto an RFID tag at predetermined time intervals until a denial is notreceived from the plurality of readers.

In operation 408, if no denial of the request is received by the firstreader from any of the readers, the RFID tag is transmitted to. Forexample, a reader which requests to transmit may transmit after notreceiving a denial of the request or after receiving acceptance totransmit from each of the readers.

In other embodiments, the readers may communicate directly with eachother via RF signal and/or network. For example, the readers may sendrequests and denials directly to each other via RF signals, or they maysend requests and denials directly to each other via a network. Anetwork may include hardwired and/or wireless components.

In another embodiment, if a denial of the request is received by anyreader, the reader receiving the denial will await the receipt of acompletion notice that will be sent from the reader sending the denialafter completion of transmission with an RFID tag. The completion noticemay be sent once or multiple times over a predetermined time. Inaddition, the completion notice may contain other information that canbe useful in reader discipline, such as which reader should transmitnext, which readers are currently waiting to transmit, etc.

In yet another embodiment, the first reader may transmit to the RFID tagif no denial is received after a predetermined amount of time haselapsed since the first reader transmitted the request to transmit. Inanother embodiment, the request may be sent a predetermined number oftimes with a pause of a predetermined length between each request, andif no denial is received after the last request, the first reader maytransmit to the RFID tag.

In one more embodiment, a request to transmit may be received fromanother reader, wherein if the first reader is transmitting or the firstreader is waiting to transmit, a denial of the other reader's requestmay be sent from the first reader. Further, the other reader may waituntil the first reader completes transmission before attempting tocommunicate with an RFID tag. In another approach, the other reader maysend requests at predetermined time intervals until a denial is notreceived from the first reader.

In still another embodiment, a reader may receive a request to transmitfrom another reader, wherein the request from the other reader mayinclude a request for priority. If the first reader is transmitting, thefirst reader may abort transmitting and the first reader may wait toretransmit to the RFID tag until after the other reader transmits withan RFID tag. In yet another approach, the first reader may send requestsat predetermined time intervals aborting transmitting until it does notreceive a denial from any other reader before transmitting to an RFIDtag. In addition, the request for priority may be in compliance with apreset priority level, such as a priority table, where differentrequests for priority have different levels have priority, such that areader transmitting at a higher priority level will not be interruptedif the request for priority received from another reader is of a lowerpriority level based on the priority table.

In one more embodiment, a first reader may receive a request to transmitfrom another reader, wherein the request from the other reader mayinclude a request for priority. If the first reader is transmitting, anda second reader is waiting to transmit, the first reader may send adenial of the other reader's request. In addition, the second reader maywait to transmit to the RFID tag until after the other reader transmitswith an RFID tag. In another approach, the second reader may transmitafter the first reader finishes transmitting, and the other reader maywait until after the second reader transmits to the RFID tag.

With reference to FIG. 5, a method 500 for coordinating readertransmissions is shown according to one embodiment. As an option, thepresent method 500 may be implemented in the context of thefunctionality and architecture of FIGS. 1, 2A, and 2B. Of course, themethod 500 may be carried out in any desired environment. It should alsobe noted that the aforementioned definitions may apply during thepresent description. In operation 502, for a first of a plurality ofreaders, it is determined whether the first reader and any other of thereaders interfere with each other.

In operation 504, a result of the determination is stored, where thefirst reader sends a request to transmit to those readers determined tointerfere with the first reader or vice versa prior to transmitting toan RFID tag. If a denial of the request is received by the first readerfrom any of the readers receiving the request, the RFID tag is nottransmitted to, and if no denial of the request is received by the firstreader from any of the readers receiving the request, the RFID tag istransmitted to. The interference may be two way or one way such that onereader interferes with the other reader but not vice versa.

In one embodiment, the denial and the request may be sent once ormultiple times over a predetermined time. In addition, the denial maycontain other information that can be useful in reader discipline, suchas which reader should transmit next, which readers are currentlywaiting to transmit, etc. Furthermore, in another embodiment, therequest may be sent a predetermined number of times with a pause of apredetermined length between each request, and if no denial is receivedafter the last request, the RFID tag may be transmitted to.

In another embodiment, the determination may be performed at startup ofat least one of the readers. Also, determination may be performed priorto any activity or transmission by the readers. For example, one or moreof the readers may be in a power-off mode or power standby mode, andwhen the reader is turned on, powered up, or otherwise activated foruse, the determination may be performed.

In yet another embodiment, previous determinations may be stored forother readers. Also, the determination may involve only the at least oneof the readers starting up in relation to the other readers. Thisincludes whether the reader starting up interferes with the otherreaders, and/or whether the other readers interfere with the readerstarting up.

In other embodiments, the first reader may store the result of thedetermination and the method may be performed for each of the readers.The storage of the determination may be accomplished with non-volatilememory included in the reader, such as flash memory, read-only memory(ROM), programmable read-only memory (PROM), etc., or with volatilememory included in the reader such as random access memory (RAM),dynamic random access memory (DRAM), static random access memory (SRAM),etc.

In still another embodiment, the readers may communicate with each othervia RF signals and/or a network, each reader being assigned a networkaddress for allowing the first reader to directly send the request totransmit to those readers determined to interfere with the first readeror vice versa. A network may include hardwired and/or wirelesscomponents.

In one more embodiment, only those readers determined to interfere withthe first reader or vice versa may receive the request from the firstreader. For example, since the transmission status of only readers thatwould interfere with transmissions from the first reader need be knownto transmit from the first reader, there is no reason to transmit therequest to all the readers. Conversely, if the first reader istransmitting, the other readers determined to interfere with the firstreader will not be able to transmit without being interfered with by thefirst reader's transmission, so these readers determined to interferewith the first reader should know of the request from the first readerto know if they can transmit.

While much of the foregoing has been described in terms of use with RFIDsystems, it is again stressed that the various embodiments may be usedin conjunction with other types of RF devices, such as receive-only RFdevices, 1- and 2-way radios, etc.

The present description is presented to enable any person skilled in theart to make and use the invention and is provided in the context ofparticular applications of the invention and their requirements. Variousmodifications to the disclosed embodiments will be readily apparent tothose skilled in the art and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the present invention. Thus, the presentinvention is not intended to be limited to the embodiments shown, but isto be accorded the widest scope consistent with the principles andfeatures disclosed herein.

In particular, various embodiments discussed herein are implementedusing the Internet as a means of communicating among a plurality ofdiscrete systems. One skilled in the art will recognize that the presentinvention is not limited to the use of the Internet as a communicationmedium and that alternative methods of the invention may accommodate theuse of a private intranet, a LAN, a WAN, a PSTN or other means ofcommunication. In addition, various combinations of wired, wireless(e.g., radio frequency) and optical communication links may be utilized.

The program environment in which a present embodiment of the inventionmay be executed illustratively incorporates one or more general-purposecomputers or special-purpose devices such facsimile machines andhand-held computers. Details of such devices (e.g., processor, memory,data storage, input and output devices) are well known and are omittedfor the sake of clarity.

It should also be understood that the techniques presented herein mightbe implemented using a variety of technologies. For example, the methodsdescribed herein may be implemented in software running on a computersystem, or implemented in hardware utilizing either a combination ofmicroprocessors or other specially designed application specificintegrated circuits, programmable logic devices, or various combinationsthereof. In particular, methods described herein may be implemented by aseries of computer-executable instructions residing on a storage mediumsuch as a carrier wave, disk drive, or computer-readable medium.Exemplary forms of carrier waves may be electrical, electromagnetic oroptical signals conveying digital data streams along a local network ora publicly accessible network such as the Internet. In addition,although specific embodiments of the invention may employobject-oriented software programming concepts, the invention is not solimited and is easily adapted to employ other forms of directing theoperation of a computer.

Various embodiments can also be provided in the form of a computerprogram product comprising a computer readable medium having computercode thereon. A computer readable medium can include any medium capableof storing computer code thereon for use by a computer, includingoptical media such as read only and writeable CD and DVD, magneticmemory, semiconductor memory (e.g., FLASH memory and other portablememory cards, etc.), etc. Further, such software can be downloadable orotherwise transferable from one computing device to another via network,wireless link, nonvolatile memory device, etc.

Moreover, any of the devices described herein, including an RFID reader,may be considered a “computer.”

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A method for coordinating reader transmissions,comprising: at a first reader, receiving from a second reader a requestto transmit to a radio frequency identification tag; in response toreceiving the request, determining whether the first reader istransmitting; and sending a denial of the request from the first readerto the second reader in response to determining that the first reader istransmitting; Wherein the second reader transmits to the radio frequencyidentification tag in response to not receiving a denial of the requestafter a predetermined amount of time has elapsed since the second readertransmitted the request to transmit.
 2. A method for coordinating readertransmissions, comprising: at a first reader, receiving from a secondreader a request to transmit to a radio frequency identification tag; inresponse to receiving the request, determining whether the first readeris transmitting; and sending a denial of the request from the firstreader to the second reader in response to determining that the firstreader is transmitting; Wherein the first and second readers receive arequest to transmit from a third reader, wherein a denial of the thirdreader's request is sent from the first and second readers when thefirst reader is transmitting and the second reader is waiting totransmit.
 3. The method of claim 2, wherein the third reader waits untilthe second reader completes transmission before attempting tocommunicate with a radio frequency identification tag.
 4. A method forcoordinating reader transmissions, comprising: from a first reader,sending to a plurality of readers a request to transmit to a radiofrequency identification tag, the request being directed to the readers;waiting for responses from the plurality of readers; not transmitting tothe radio frequency identification tag in response to the first readerreceiving a denial of the request from any of the readers; andtransmitting to the radio frequency identification tag in response tothe first reader not receiving a denial of the request from any of thereaders; Comprising: receiving a request to transmit from anotherreader, wherein a denial of the other reader's request is sent from thefirst reader when the first reader is transmitting or the first readeris waiting to transmit.
 5. The method of claim 4, wherein the otherreader waits until the first reader completes transmission beforeattempting to communicate with a radio frequency identification tag. 6.A method for coordinating reader transmissions, comprising: for a firstof a plurality of readers, determining whether the first reader and anyother of the readers interfere with each other; and storing a result ofthe determination; wherein the first reader sends a request to transmitto those readers determined to interfere with the first reader or viceversa prior to transmitting to a radio frequency identification tag, therequest to transmit being directed to those readers determined tointerfere with the first reader or vice versa; wherein the first readerdoes not transmit to the radio frequency identification tag in responseto the first reader receiving a denial of the request from any of thereaders the request was sent to; and wherein the first reader transmitsto the radio frequency identification tag in response to the firstreader not receiving a denial of the request from any of the readers therequest was sent to.
 7. The method of claim 6, wherein the determinationis performed in response to activating at least one of the readers. 8.The method of claim 7, wherein previous determinations are stored forother readers, wherein the determination involves only the at least oneof the readers activating in relation to the other readers.
 9. Themethod of claim 6, wherein the first reader stores the result of thedetermination.
 10. The method of claim 6, wherein the method isperformed for each of the readers.
 11. The method of claim 6, whereinthe readers communicate with each other via a network, each reader beingassigned a network address for allowing the first reader to directlysend the request to transmit to those readers determined to interferewith the first reader or vice versa.
 12. The method of claim 6, whereinonly those readers determined to interfere with the rust reader err viceversa receive the request from the fast reader.
 13. A system,comprising: a processing circuit; memory coupled to the processingcircuit; and an antenna coupled to the processing circuit, wherein theprocessing circuit is configured to: determine whether a first of aplurality of readers and any other of the readers interfere with eachother, store a result of the determination; store a request to transmitfrom the first reader to those readers determined to interfere with thefirst reader or vice versa prior to transmitting to a radio frequencyidentification tag, the request to transmit being directed to thosereaders determined to interfere with the first reader or vice versa; nottransmit to the radio frequency identification tag in response to thefirst reader receiving a denial of the request from any of the readersreceiving the request; and transmit to the radio frequencyidentification tag in response to the first reader not receiving adenial of the request from any of the readers receiving the request. 14.A computer program product comprising a non-transitory computer readablemedium having computer code thereon, which when executed by a readercauses the reader to: determine whether a first of a plurality ofreaders and any other of the readers interfere with each other; andstore a result of the determination; send a request to transmit from thefirst reader to those readers determined to interfere with the firstreader or vice versa prior to transmitting to a radio frequencyidentification tag, the request to transmit being directed to thosereaders determined to interfere with the first reader or vice versa; nottransmit to the radio frequency identification tag in response to thefirst reader receiving a of the request from any of the readersreceiving the request; and transmit to the radio frequencyidentification tag in response to the first reader not receiving adenial of the request from any of the readers receiving the request.